Fuel cell control system and method

ABSTRACT

When an electric power generation demand occurs for a fuel cell stack  1 , an electric power stored in a battery  8  is commenced to be supplied to a load (step S 3 ) followed by setting a period (step S 2 ), in which a sensor signal from a fuel cell system  10  is held in a preceding value, in a subtraction timer, and when discrimination is made (step S 5 , step S 6 ) that the fuel cell system  10  is started up and each pressure is stabilized from a sensor signal from the fuel cell system  10 , the electric power generated in the fuel cell stack  1  is commenced to be supplied to the load (step S 8 ) followed by setting the period, in which the sensor signal from the fuel cell system  10  is held in the preceding value, in the subtraction timer (step S 7 ).

TECHNICAL FIELD

[0001] The present invention relates to a control system and method of afuel cell that generates an electric power for driving a drive motor ofa fuel cell powered vehicle.

BACKGROUND ART

[0002] Normally, in order to increase an electric power generatingefficiency of a fuel cell stack in a fuel cell system, there is a needfor increasing an electric power voltage of the fuel cell stack.However, if an electric power supply formed by the fuel cell stack isturned on or off under a condition where an output voltage of the fuelcell stack is increased, in a case where an initial resistance value ofa connection equipment of the fuel cell stack is low, it is probablethat a large electric current flows through connecting parts.

[0003] On the contrary, a fuel cell system described in Japanese PatentProvisional Publication No. 2002-063925 is configured to prevent a highvoltage from being applied to equipments of a direct current electricpower system by providing a shut-off circuit for thereby protectingconnecting equipments of a fuel cell stack.

DISCLOSURE OF THE INVENTION

[0004] Further, in a normal fuel cell system, during electric powergeneration of the fuel cell stack, first, it is necessary to supply fuelgas and oxidizing gas under a state to enable the fuel cell stack togenerate the electric power and, if these gas pressures exceeds givenlevels, electric power generation is commenced to allow electric currentto be taken out from the fuel cell stack.

[0005] However, with such a fuel cell system, since a large electriccurrent flows at the same time that the electric power is taken out fromthe fuel cell stack, there seems to be a probability in that detectionnoises occur even though a pressure sensor for fuel gas and atemperature sensor do not form equipments of a direct current electricpower system with respect to an electric current system of the fuel cellsystem. Thus, if large noises occur in a sensor signal related to, forinstance, a fuel gas pressure, erroneous discrimination is made that alarge differential pressure is created between fuel gas and oxidizinggas and, further, erroneous discrimination is made that the differentialpressure between fuel gas and oxidizing gas falls in a high value thatinduces an operational inability, providing a probability of resultantinterruption of the fuel cell system per se.

[0006] Thus, the present invention has been made in view of the aboveactual states and a first aspect of the present invention is a fuel cellcontrol system comprising a fuel cell stack, a fuel cell system takingout an electric power generated by the fuel stack to be supplied to aload, and a control section controlling an electric power generatingoperation of the fuel cell stack based on a sensor signal inputted froma sensor disposed in the fuel cell system, wherein the control sectioncontrols the fuel cell system such that, during startup of the fuel cellsystem, a gas supply pressure of the fuel cell stack in compliance withthe sensor signal inputted from the sensor is discriminated to bestabilized at an electric power generation start pressure of the fuelcell stack, a time duration, involving an electric power taking outstart timing at which an electric power is taken out from the fuel cellstack, is set as a period in which the sensor signal is held in apreceding value and gas supply to the fuel cell stack is commenced basedon the sensor signal held in the preceding value.

[0007] A second aspect of the present invention is a fuel cell controlsystem comprising a fuel cell stack, a fuel cell system taking out anelectric power generated by the fuel stack to be supplied to a load, anda control section controlling an electric power generating operation ofthe fuel cell stack based on a sensor signal inputted from a sensordisposed in the fuel cell system, wherein the control section controlsthe fuel cell system such that, during stop of the fuel cell system, agas supply pressure of the fuel cell stack in compliance with the sensorsignal inputted from the sensor is discriminated to be stabilized, atime duration, involving an electric power taking out start timing atwhich an electric power is taken out from the fuel cell stack, is set asa period in which the sensor signal is held in a preceding value and gassupply to the fuel cell stack is interrupted based on the sensor signalheld in the preceding value.

[0008] A third aspect of the present invention is a fuel cell controlmethod comprising calculating a gas supply pressure related to a fuelcell stack from a sensor signal inputted from a sensor disposed in afuel cell system during startup of the fuel cell system, discriminatingthat the gas supply pressure is stabilized at an electric powergeneration start pressure of the fuel cell stack, setting a timeduration, involving an electric power taking out start timing at whichan electric power is taken out from the fuel cell stack, as a period inwhich the sensor signal is held in a preceding value, and controllingthe fuel cell system so as to begin gas supply to the fuel cell stackbased on the sensor signal held in the preceding value.

[0009] A fourth aspect of the present invention is a fuel cell controlmethod comprising calculating a gas supply pressure related to a fuelcell stack from a sensor signal inputted from a sensor disposed in afuel cell system during stop of the fuel cell system, discriminatingthat the gas supply pressure is stabilized at an electric powergeneration start pressure of the fuel cell stack, setting a timeduration, involving an electric power taking out start timing at whichan electric power is taken out from the fuel cell stack, as a period inwhich the sensor signal is held in a preceding value; and controllingthe fuel cell system so as to stop gas supply to the fuel cell stackbased on the sensor signal held in the preceding value.

BRIEF DESCRIPTION OF DRAWINGS

[0010]FIG. 1 is a block diagram illustrating a structure of a controldevice of a fuel cell system to which the present invention is applied.

[0011]FIG. 2 is a block diagram illustrating a concrete structure of thefuel cell system.

[0012]FIG. 3 is a flowchart illustrating an operational sequence of anelectric power generation startup control operation to be performed by asystem control section for starting up the fuel cell system to startelectric power generation.

[0013]FIG. 4 is a flowchart illustrating an operational sequence of afuel cell system monitoring control operation to be performed by thesystem control section for monitoring a status of the fuel cell system.

[0014]FIG. 5 is a flowchart illustrating an operational sequence of anelectric power generation stop control operation to be performed by thesystem control section for stopping the electric power generation of thefuel cell system.

[0015]FIGS. 6A to 6G are views illustrating an effect of the controldevice of the fuel cell system to which the present invention isapplied, with FIG. 6A showing operation of a battery J/B, FIG. 6Bshowing operation of a stack J/B, FIG. 6C showing a sensor signalproduced by a fuel pressure sensor, FIG. 6D showing a sensor signalproduced by a coolant water sensor, FIG. 6E showing a period in which apreceding value is held by the system control section, FIG. 6Frepresenting a time change of a differential pressure between a fuelpressure gas and a coolant water pressure detected by the system controlsection and FIG. 6G representing a time change of the differentialpressure between the fuel pressure gas and the coolant water pressuredetected by a system control section of a comparison.

BEST MODE FOR CARRYING OUT THE INVENTION

[0016] Hereinafter, an embodiment according to the present invention isdescribed with reference to the drawings.

[0017] The present invention is applied to a control device 100 of afuel cell system structured as shown in FIG. 1. The control system 100of the fuel cell system is installed, for instance, in a fuel cellpowered vehicle having a fuel cell stack 1 a as a drive source. The fuelcell stack 1 serves to achieve electrochemical reaction between fuelgas, such as hydrogen or the like, and oxidizing gas containing oxygenby means of electrolyte, thereby directly taking out electric power fromelectrodes.

[0018] In the control system 100 of such a fuel cell system, the fuelcell stack 1 is connected to a stack J/B (junction box) 3 and anelectric power control section 4 with high voltage line 2. An electricpower output voltage generated at the fuel cell stack 1 is supplied tothe stack J/B 3 whereupon the output voltage is regulated by theelectric power control section 4 and supplied to a drive motor 5 and abattery J/B 6. By so doing, the drive motor 5 produces an output torquefor driving the fuel cell powered vehicle in dependence on control of amotor controller 7. In the meantime, the output voltage supplied to thebattery J/B 6 is supplied to and stored in a battery (secondary battery)8.

[0019] Further, the electric power stored in the battery 8 is dischargedin accordance with control of a battery controller 9, with dischargedelectric power being supplied to the drive motor 5 via the battery J/B6.

[0020] Furthermore, the control system 100 of the fuel cell system iscomprised of a fuel cell system 10, permitting the fuel cell stack 1 toperform electric power generation, which is operated in accordance withcontrol of a system control section 11. The system control section 11drivingly controls the fuel cell system 10 depending on a driving demandof the drive motor 5 from an external source to initiate or interruptelectric power generation of the fuel cell stack 1 for controlling theelectric power to be generated by the fuel cell stack 1. When this takesplace, the system control section 11 is applied with sensor signals fromvarious sensors, described later, which are located in the fuel cellsystem 10, and controls the fuel cell system 10.

[0021] Moreover, the system control section 11 controls the electricpower control section 4 to allow the electric power, delivered from thestack J/B 3, to be regulated and to be supplied to the battery J/B 6 andthe drive motor 5 and controls the battery controller 9 for controllingcharging and discharging of the battery 8, while also controlling themotor controller 7 to control a drive torque of the drive motor 5.

[0022] In the control device 100 of the fuel cell system, although adetail is described below, the system control section 11 executes thefollowing:

[0023] (1) electric power generation startup control operation forstarting up the fuel cell stack 1 to initiate electric power generation;

[0024] (2) fuel cell system monitoring control operation for monitoringoperation of the fuel cell system 10; and

[0025] (3) electric power generation stop control operation for stoppingthe fuel cell stack 1 to terminate electric power generation of the fuelcell stack 1.

[0026] [Concrete Structure of Fuel Cell System 10]

[0027] Now, a concrete structure of the fuel cell system 10 is describedwith reference to FIG. 2.

[0028] The fuel cell stack 1 includes a fuel electrode 1 a to which fuelgas is supplied and an air electrode 1 b to which air is supplied, withthe fuel electrode 1 a and the air electrode 1 b being joined to oneanother via a solid polymer film where respective ions transfer by meansof medium composed of moisture to be brought into contact with oneanother to generate electric power. Also, the fuel cell stack 1 isinternally equipped with a coolant water conduit for appropriatelymaintaining a fuel cell temperature.

[0029] Connected to such a fuel cell stack 1 via a hydrogen deliverypipe are a fuel storage tank 21, a fuel gas pressure control valve 22,an ejector recirculation unit 23 and a condensed water recovery unit 24,thereby supplying hydrogen to the fuel electrode 1 a as fuel gas.

[0030] Fuel gas is compressed in the fuel storage tank 21 to remainunder a high pressure and is reduced in pressure by the fuel gaspressure control valve 22 to be supplied to the ejector recirculationunit 23. Also, the present embodiment has been shown in conjunction witha case where the fuel storage tank 21 and the fuel pressure controlvalve 22 are in direct communication with one another, in addition,another valve for reducing pressure may be located in a midway betweenthe fuel storage tank 21 and the fuel gas pressure control valve 22.

[0031] Fuel gas passing through the fuel gas pressure control valve 22is supplied to the ejector recirculation unit 23 through a recirculationdelivery pipe and mixed with fuel gas that passes through the fuelelectrode 1 a and supplied through a condensed water recovery unit 25,whereupon mixed fuel gas is delivered to the condensed water recoveryunit 24 and supplied to the fuel electrode 1 a. When this takes place,the condensed water recovery units 24, 25 serve to condense steamthrough a radiation heat cooling effect resulting from delivery pipesextending through the fuel cell stack 1 from the ejector recirculationunit 23 to form moisture that is separated from fuel gas, with resultingfuel gas being supplied to the fuel cell stack 1 and the ejectorrecirculation unit 23.

[0032] Further, in a case where the electric power generation demand forthe fuel cell stack 1 rapidly drops or the operation of the fuel cellstack 1 is interrupted, fuel gas which is not consumed by the fuel cellstack 1 is passed through a fuel gas exhaust valve 26, locateddownstream of a fuel gas stream of the fuel cell stack 1 and is, forinstance, combusted in a hydrogen combustor and subsequently dischargedto the outside. Also, although there are many probabilities where, innormal practice, the fuel gas exhaust valve 26 may include an ON/OFFvalve to provide an ease of control, it may include a flow rate andpressure control valve whose opening degree is controllable.

[0033] Here, the system control section 11 reads in a sensor signal(indicated by an arrow L1) delivered from a fuel pressure sensor 29disposed on the fuel gas delivery pipe between the condensed waterrecovery unit 24 and the fuel electrode 1 a such that the fuel gaspressure supplied to the fuel electrode 1 a is detected to control anactuator 27 which opens or closes the fuel gas pressure control valve 22(as indicated by an arrow L2). By so doing, the flow rate and pressureof fuel gas to be supplied to the fuel electrode 1 a are regulated and,additionally, an actuator 28 for opening and closing the fuel gasexhaust valve 26 is drivingly controlled (as shown by an arrow L3).

[0034] In the meantime, air is taken out from the atmosphere by acompressor 30 and compressed to be fed into an air delivery pipe. Here,since air compressed by the compressor 30 is raised at a hightemperature, for the purpose of permitting reaction to take place in thefuel cell stack 1 at a high efficiency, air is cooled by an air cooler31 mounted at an air inlet of the fuel cell stack 1 and supplied to theair electrode 1 b. And, since air with oxygen constituent being consumedat the air electrode 1 b of the fuel cell stack 1 while containingresidual oxygen contains moisture resulting from reaction in the fuelcell stack 1, moisture is recovered in a water recovery unit 32 and,thereafter, air is expelled to the atmosphere through an air pressureregulator valve 33. Also, connected to an air exhaust side of the airelectrode 1 b is an air purge valve 34 that is rendered opened during anair purge mode.

[0035] Here, the system control section 11 drivingly controls thecompressor 30 to regulate the air flow rate (as shown in an arrow L4)and reads in a sensor signal (as shown in an arrow L5) delivered from anair pressure sensor 37 disposed in an air delivery pipe between the aircooler 31 and the air electrode 1 b to detect the air pressure suppliedto the air electrode 1 b so as to control an actuator 35 (as shown by anarrow L6) for opening and closing the air pressure regulator valve 33such that the air pressure is regulated to allow the air pressure to beequalized with the fuel gas pressure. When this occurs, the systemcontrol section 11 controls the actuator 35 such that, when intended toincrease the air pressure, the air pressure regulator valve 33 isoperated in a closing direction. Also, the system control section 11drivingly controls an actuator 36 (as shown by an arrow L7) such that,during a purge mode of the fuel electrode 1 b, the air purge valve 34 isoperated in an opening direction.

[0036] The fuel cell system 10 employs ethylene glycol with high boilingtemperature as coolant water of the fuel cell stack 1. This coolantwater is drawn by a pump 38 to be fed from a reservoir tank 39 into acoolant water circulation passage and fed into the fuel cell stack 1 viaa temperature regulator 40 that operates in combination with a radiatorand a fan to maintain the temperature at a constant level. By so doing,the temperature of the fuel cell stack 1 is regulated. Coolant waterpassage through a coolant water delivery pipe in the fuel cell stack 1is heated by electric power generation of the fuel cell stack 1 andaccumulated in the reservoir tank 39 prior to being circulated to thepump 38. This provides functions such as absorption of rapid pressurevariation such as water hummer or an accumulator for the pump flow rate.

[0037] Further, disposed in the close proximity to the coolant inlet ofthe fuel cell stack 1 in the coolant water circulation passage are acoolant water pressure sensor 41 that detects a coolant water pressureand a coolant water temperature sensor 42 that detects a coolant watertemperature. Also, although the present embodiment has been shown withreference to a case where the coolant water pressure sensor 41 and thecoolant water temperature sensor 42 are disposed at the coolant inlet ofthe fuel cell stack 1, the present embodiment is not restricted theretoand these may be located at a coolant water outlet of the fuel cellstack 1.

[0038] Here, the system control section 11 reads in a sensor signaldelivered from the coolant water pressure sensor 41 (as shown by anarrow L8) such that the pressure of coolant water supplied to the fuelcell stack 1 is detected to control the discharge flow rate of the pump38 (as shown by an arrow L9) in dependence on the electric power outputof the fuel cell stack 1. Also, other control technique for the coolantwater pressure may include an orifice valve located in the coolant watercirculation passage through which pressure control of coolant water isperformed.

[0039] [Control Operation by System Control Section]

[0040] Next, various control operations to be performed by the systemcontrol section 11 of the control device 100 of the fuel cell system ofthe structure previously mentioned are described.

[0041] (1) Electric Power Generation Startup Control Operation

[0042] First, an operational sequence of electric power generationstartup control operation of the system control section 11 for startingup the fuel cell stack 1 to initiate electric power generation isdescribed with reference to a flowchart of FIG. 3. The electric powergeneration startup control operation is executed by the system controlsection 11 in synchronism with an internal timer of, for instance, a CPU(Central Processing Unit) equally divided time durations each for, forexample, 10 msec.

[0043] For instance, if an electric power generation demand for the fuelcell stack 1 is inputted into the system control section 11 fromoutside, first in step S1, discrimination is made to see whetherinsulation resistance of an electric power system is extremely large todiscriminate as to whether electric shock or short circuiting is apt totake place when the power supply of the electric power system is turnedon. If it is discriminated that no electric shock or short circuitingoccur when insulation resistance of a high voltage line 2 exceeds agiven value and the electric power source is turned on, operationproceeds to step S2.

[0044] In step S2, prior to turning on the power supply, composed of thebattery 8, by means of the battery J/B 6, a subtraction timer valueTIM_chk1 for holding a preceding value of a sensor signal valuedelivered from the fuel supply system 10 is set to an initial valueTIM_init1 (for instance, 10) to begin holding of the preceding values ofrespective sensor signal values (indicated by arrows L1, L2, L3 in FIG.2) delivered from the fuel pressure sensor 29, the air pressure sensor37 and the coolant water pressure sensor 41, allowing operation toproceed to step S3.

[0045] Here, the initial value TIM_init1 is set to have a time durationinvolving a startup timing (start time) at which electric power is takenout from the battery 8 in step S3 described later. In particular, theinitial value TIM_init1 is set to have a period during which it isprobable for noises to occur in the sensor signal when the electricpower is taken out from the battery 8 and have a value that reaches zeroat a time before various sensor signals are detected in step S6described below.

[0046] In step S3, the battery controller 9 is controlled by the systemcontrol section 11 to turn on the battery J/B 6 and, in step S4,discrimination is made to see whether the voltage of the high voltageline 2 of the electric power system reaches a given range. If the systemcontrol section 11 discriminates that the electric power system voltageof the high voltage line 2 reaches the given range, operation proceedsto step S5. This given range means a range excluding a high voltageoccurring when the electric power stored in the battery 8 begins to besupplied to the high voltage line 2 and is set to a range in which thevoltage applied to the high voltage line 2 is stabilized.

[0047] In preparation for the following electric power generationstartup of the fuel cell stack 1 in step S5, the system control section11 starts up various parts forming the fuel cell system 10 and operationproceeds to step S6. In particular, the system control section 11 startsup peripheral units of the fuel cell stack 1, such as the compressor 30for supplying air, the ejector circulation unit 23 for supplying fuelgas, the pump 38 for circulating coolant water and the temperatureregulator 40.

[0048] In step S6, the system control section 11 is applied with thesensor signals (the arrows L1, L5, L8) from the fuel pressure sensor 29,the air pressure sensor 37 and the coolant water pressure sensor 41 anddiscriminates to see whether the hydrogen pressure, the air pressure andthe coolant water pressure remain at respective stabilized levelssufficient for starting electric power generation of the fuel cell stack1. If the system control section 11 discriminates that fluctuations inthe respective sensor signals, resulting from the start at which theelectric power is taken out from the battery 8, converge and therespective pressures stand stabilized, then, operation proceeds to stepS7.

[0049] In step S7, for the purpose of setting the subtraction timerdifferent from that of step S2, a subtraction timer value TIM_chk2 forholding the preceding value of the sensor signal value is set to aninitial value TIM_init2 (for instance, 10) to begin holding of thepreceding values of respective sensor signal values (indicated by arrowsL1, L2, L3 in FIG. 2) delivered from the fuel pressure sensor 29, theair pressure sensor 37 and the coolant water pressure sensor 41,allowing operation to proceed to step S8, and controlling the stack J/B3 and the electric power control section 4 begins taking out theelectric power from the fuel cell stack 1 while terminating operation.

[0050] Here, the initial value TIM_init2 is set to have a time durationinvolving a startup timing (start time) at which electric power is takenout from the fuel cell stack 1 in step S8 described later. Inparticular, the initial value TIM_init2 is set to have a period duringwhich it is probable for noises to occur in the sensor signal when theelectric power is taken out from the fuel cell stack 1 and have a valuethat reaches zero at a time before various sensor signals are detectedin step S6 described below.

[0051] (2) Fuel Cell System Monitoring Control Operation

[0052] Next, an operational sequence of the system control section 11for monitoring control operation of the fuel cell system for monitoringa status of the fuel cell system 10 after the fuel cell system 10 hasbeen started up upon execution of the above-described fuel cell systemmonitoring control operation is described with reference to a flowchartof FIG. 4.

[0053] During fuel cell system monitoring control operation,independently of electric power generation startup control operation, anabnormality is monitored at the same time that the fuel cell system 10has been stared up.

[0054] First in step S11, upon discrimination of the system controlsection 11 to see whether the subtraction timer value TIM_chk1, that isset in step S2, and the subtraction timer value TIM_chk2 set in step S7do not fall in zero, the system control section 11 discriminates to seewhether the sensor signal value remains in the period in which thepreceding value is held.

[0055] If the system control section 11 discriminates that the sensorsignal value does not fall in the period in which the preceding value isheld, then, operation proceeds to step S12 and is applied with thesensor signals (the arrows L1, L5, L8) delivered from the fuel pressuresensor 29, the air pressure sensor 37 and the coolant water pressure 41whereupon operation proceeds to step S14.

[0056] In the meantime, if the system control section 11 discriminatesthat the sensor signal value falls in the period in which the precedingvalue is held, operation proceeds to step S13 and respective subtractiontimer values, which are set in step S2 and step S7, are subtracted whileproceeding operation to step S14. That is, the system control section 11performs operation of step S14 while holding the sensor signals in therespective preceding values.

[0057] In step S14, using the respective sensor signal values, thesystem control section 11 discriminates to see whether a differentialpressure between the fuel gas pressure and the air pressure, adifferential pressure between the air pressure and the coolant waterpressure and a differential pressure between the coolant water pressureand the fuel gas pressure fall in given values and, if it isdiscriminated that the respective differential pressures fall in therespective given values, then, operation is terminated. Here, the givenvalues to be compared with the respective differential pressures are setto differential pressure values, during system designs, which haveprobabilities to cause the fuel cell stack 1 to be damaged due to therespective pressure differences.

[0058] In the meantime, if the system control section 11 discriminatesthat either one of the differential pressures does not fall in the givenvalue, the system control section 11 judges that either one of thepressure difference has an abnormal value and there is a probability ofoccurrence of the damages in the fuel cell stack 1, interruptingoperations of various parts forming the fuel cell system 10 to stopsupply of fuel while terminating operation.

[0059] (3) Electric Power Generation Stop Control Operation

[0060] Next, an operational sequence of the system control section 11for implementing electric power generation stop control operation tostop electric power generation of the fuel cell stack 1 is describedwith reference to a flowchart of FIG. 5.

[0061] For instance, if a request for stop of electric power generationof the fuel cell stack 1 is inputted to the system control section 11from outside, first in step S21, the system control section 11 isapplied with the respective sensor signals (indicated by the arrows L1,L5, L8) to discriminate whether the fuel gas pressure, the air pressureand the coolant water pressure remain in given ranges and, if it isdiscriminated that these remain in the given ranges, operation proceedsto step S22.

[0062] In step S22, the system control section 11 sets the subtractiontimer value TIM_chk2, related to the fuel cell stack 1, to the initialvalue TIM_init2 to start subtraction of the subtraction timer valuewhile holding the sensor signal values, and operation proceeds to stepS23.

[0063] Here, the initial value TIM_init2 is set to have a time periodinvolving a stop timing (stop time) for stopping the electric power frombeing taken out of the fuel cell stack 1 in step S23. In particular, theinitial value TIM_init2 is set to have a period that has a probabilityof noises occurring in the sensor signal due to stop of the electricpower being taken out from the fuel cell stack 1.

[0064] In step S23, the stack J/B 3 is controlled by the system controlsection 11 to cut out the voltage to be supplied to the electric powercontrol section 4 from the fuel cell stack 1 and operation proceeds tostep S24, interrupting operations of various parts forming the fuel cellstack 10 while proceeding operation to step S25.

[0065] In step S25, the system control section 11 discriminates to seewhether the electric power generation of the fuel cell stack 1 in stepS24 to cause the electric power system voltage in the high voltage line2 to drop to allow the electric power system voltage in the high voltageline 2 to fall in a given range. If the system control section 11discriminates that the electric power system voltage in the high voltageline 2 falls in the given range, operation proceeds to step S26.

[0066] In step S26, the subtraction timer value TIM_chk1, related to thebattery 8, is set to the initial value TIM_init1 by the system controlsection 11 to begin subtraction of the subtraction timer value to allowoperation to proceed to step S27, thereby blocking the voltage frombeing supplied from the battery to the drive motor 5 via the battery J/B6 and terminating operation.

[0067] Here, the initial value TIM_init1 to be determined for thesubtraction timer value TIM_chk1 is set to have a time durationinvolving a stop timing (stop time) to interrupt the electric powerbeing taken out from the battery in step S27. In particular, the initialvalue TIM_init1 is set to have a period that has a probability of noisesoccurring in the sensor signal due to stop of the electric power beingtaken out from the battery 8.

[0068] Next, a control effect provided by the system control section 11for performing such control operation is described with reference toFIGS. 6A to 6G.

[0069] According to the control device 100 of the fuel cell systemequipped with the system control section 11 which performs such controloperation, if the electric power begins to be taken out from the battery8 at a time T1 (see FIG. 6A), noises occur in the sensor signal (thearrow L1) delivered from the fuel pressure sensor 29 and the sensorsignal (the arrow L8) delivered from the coolant water pressure sensor41 (see FIGS. 6C, 6D). This is because of the fact that noises of theelectric power system connecting the battery 8 and the drive motor 5affect on control lines which connect the system control section 11 andthe fuel cell system 10.

[0070] When this takes place, although, in the fuel cell system 10,there is no occurrence in rapid fluctuation in the differential pressurebetween the fuel gas pressure and the coolant water pressure, the systemcontrol section 11 comes to be applied with the sensor signals withprofiles shown in FIGS. 6C and 6D.

[0071] On the contrary, since the presently filed embodiment permits thesensor signals to be held in the respective preceding values in step S2prior to electrical connection between the battery 8 and the drive motor5 in step S3, as shown in FIG. 3, during the electric power generationstartup control operation, even if noises occur in the sensor signal instep S3, the resulting signal value is not effective to control the fuelcell system 10. That is, in the system control section 11, as shown inFIG. 6F, since the sensor signal value appearing in step S2 is used,control of the fuel cell system 10 is performed under a condition whereno differential pressure exists between the fuel gas pressure and thecoolant water pressure.

[0072] In a case where, as comparison with respect to the presentlyfiled embodiment, if the sensor signal, associated with electricalconnection between the battery 8 and the drive motor 5, is used as itis, as shown in FIG. 6G, there is a probability in which the systemcontrol section 11 makes an erroneous discrimination that thedifferential pressure between the fuel gas pressure and the coolantwater pressure becomes large to stop operation of the fuel cell system10 and, further, stops the start for electric power generation of thefuel cell stack 1.

[0073] Namely, since the presence of excessively increasing pressuredifference between fuel gas and coolant water to be supplied to the fuelcell stack 1 leads the fuel cell stack 1 to be damaged, the systemcontrol section 11 monitors the differential pressures at all times andstops the fuel cell system 10 when detecting that the differentialpressure increases to an extent causing the fuel cell stack 1 to bedamaged.

[0074] Further, even if subsequent to electrical connection between thebattery 8 and the drive motor 5, the fuel cell stack 1 generateselectric power at time T2 and the fuel cell stack 1 and the drive motor5 are electrically connected (see FIG. 6B), the presently filedembodiment controls the fuel cell system 10 under a condition with norecognition of the differential pressure, whereas comparison has aprobability in which the differential pressure is recognized andoperation of the fuel cell system 10 is stopped.

[0075] Consequently, according to the control device 100 of the fuelcell system of the presently filed embodiment, in a case where the fuelcell stack 1 and the battery 8, and the drive motor 5 are electricallyconnected to allow the electric power system power source to be turnedon during the electric power generation startup control operation, evenif noises occur in the sensor signal vales to be supplied from the fuelcell system 10 to the system control section 11, it is possible toprevent the fuel cell system 10 from making erroneous discrimination inthat the differential pressure between fuel gas and coolant waterbecomes large.

[0076] Furthermore, since the control device 100 of such a fuel cellsystem performs the fuel cell system monitoring control operation underthe condition where the sensor signals are held in the preceding valuesfor the period during which the subtraction timer value reaches zeroafter the electric power system has been turned on, it is possible topreclude erroneous discrimination in that a large pressure differenceoccurs in the period when noises occur in the sensor signals due topower supply turning-on of the electric power system.

[0077] Moreover, according to the control device 100 of the fuel cellsystem, even if noises occur in the sensor signal values wheninterrupting operation of the electric power system during electricpower generation startup control operation, it is possible to precludethe fuel cell system 10 from making erroneous discrimination in that thedifferential pressure between fuel gas and coolant water is large.

[0078] In addition, according to the control device 100 of the fuel cellsystem, since discrimination is made that, prior to holding therespective sensor signals in the preceding values, the fuel gaspressure, the air pressure and the coolant water pressure are adequatelystabilized in a state necessary for starting the electric powergeneration of the fuel cell stack 1, it is possible to accuratelyperform control of a status where pressures assume values for the startof the electric power generation using the sensor signals delivered fromthe respective sensors, thereby reliably precluding the fuel cell stack1 from being damaged due to an increase in each pressure differenceduring such a period.

[0079] Also, the above-described embodiment forms an example of thepresent invention. For this reason, the present invention is not limitedto the presently filed embodiment set forth above and, of course, whenthe invention is embodied in other forms, various modifications may bemade in compliance with designs without departing from the technicalconcept of the resent invention.

[0080] The entire content of Japanese Application No. P2002-178975 witha filing date of Jun. 19, 2002 is herein incorporated by reference.

[0081] Although the present disclosure has been described above byreference to certain embodiments of the invention, the invention is notlimited to the embodiments described above and modifications will occurto those skilled in the art, in light of the teachings. The scope of theinvention is defined ith reference to the following claims.

INDUSTRIAL APPLICABILITY

[0082] According to the present invention, since during a start fortaking out electric power from a fuel cell stack 1 and a stop of a fuelcell system, sensor signals are held in preceding values under acondition where gas supply pressures are stabilized, it is possible toprevent erroneous diagnosis from being caused by noises even inoccurrence of noises in the sensor signals during the start and stop ofthe electric power being taken out from the fuel cell stack.

1. A fuel cell control system comprising: a fuel cell stack; a fuel cellsystem taking out an electric power generated by the fuel stack to besupplied to a load; and a control section controlling an electric powergenerating operation of the fuel cell stack based on a sensor signalinputted from a sensor disposed in the fuel cell system, wherein thecontrol section controls the fuel cell system such that, during startupof the fuel cell system, a gas supply pressure of the fuel cell stack incompliance with the sensor signal inputted from the sensor isdiscriminated to be stabilized at an electric power generation startpressure of the fuel cell stack, a time duration, involving an electricpower taking out start timing at which an electric power is taken outfrom the fuel cell stack, is set as a period in which the sensor signalis held in a preceding value and gas supply to the fuel cell stack iscommenced based on the sensor signal held in the preceding value.
 2. Thefuel cell control system according to claim 1, wherein the controlsection controls the fuel cell system so as to begin gas supply to thefuel cell stack after an elapse of a given time interval from a start oftaking out electric power stored in a secondary battery.
 3. A fuel cellcontrol system comprising: a fuel cell stack; a fuel cell system takingout an electric power generated by the fuel stack to be supplied to aload; and a control section controlling an electric power generatingoperation of the fuel cell stack based on a sensor signal inputted froma sensor disposed in the fuel cell system, wherein the control sectioncontrols the fuel cell system such that, during stop of the fuel cellsystem, a gas supply pressure of the fuel cell stack in compliance withthe sensor signal inputted from the sensor is discriminated to bestabilized, a time duration, involving an electric power taking outstart timing at which an electric power is taken out from the fuel cellstack, is set as a period in which the sensor signal is held in apreceding value and gas supply to the fuel cell stack is interruptedbased on the sensor signal held in the preceding value.
 4. A fuel cellcontrol system comprising: a fuel cell stack; a fuel cell system takingout an electric power from the fuel stack to be supplied to a load; andcontrol means controlling an electric power generating operation of thefuel cell stack based on a sensor signal inputted from a sensor disposedin the fuel cell system, wherein the control means controls the fuelcell system such that, during startup of the fuel cell system, a gassupply pressure of the fuel cell stack in compliance with the sensorsignal inputted from the sensor is discriminated to be stabilized at anelectric power generation start pressure of the fuel cell stack, a timeduration, involving an electric power taking out start timing at whichan electric power is taken out from the fuel cell stack, is set as aperiod in which the sensor signal is held in a preceding value and gassupply to the fuel cell stack is commenced based on the sensor signalheld in the preceding value.
 5. A fuel cell control system comprising: afuel cell stack; a fuel cell system taking out an electric powergenerated by the fuel stack to be supplied to a load; and control meanscontrolling an electric power generating operation of the fuel cellstack based on a sensor signal inputted from a sensor disposed in thefuel cell system, wherein the control means controls the fuel cellsystem such that, during stop of the fuel cell system, a gas supplypressure of the fuel cell stack in compliance with the sensor signalinputted from the sensor is discriminated to be stabilized, a timeduration, involving an electric power taking out start timing at whichan electric power is taken out from the fuel cell stack, is set as aperiod in which the sensor signal is held in a preceding value and gassupply to the fuel cell stack is interrupted based on the sensor signalheld in the preceding value.
 6. A fuel cell control method comprising:calculating a gas supply pressure related to a fuel cell stack from asensor signal inputted from a sensor disposed in a fuel cell systemduring startup of the fuel cell system; discriminating that the gassupply pressure is stabilized at an electric power generation startpressure of the fuel cell stack; setting a time duration, involving anelectric power taking out start timing at which an electric power istaken out from the fuel cell stack, as a period in which the sensorsignal is held in a preceding value; and controlling the fuel cellsystem so as to begin gas supply to the fuel cell stack based on thesensor signal held in the preceding value.
 7. A fuel cell control methodcomprising: calculating a gas supply pressure related to a fuel cellstack from a sensor signal inputted from a sensor disposed in a fuelcell system during stop of the fuel cell system; discriminating that thegas supply pressure is stabilized at an electric power generation startpressure of the fuel cell stack; setting a time duration, involving anelectric power taking out start timing at which an electric power istaken out from the fuel cell stack, as a period in which the sensorsignal is held in a preceding value; and controlling the fuel cellsystem so as to stop gas supply to the fuel cell stack based on thesensor signal held in the preceding value.